A car driver's airbag is designed, in the event of a head-on or glancing collision (e.g. with an obstacle at 30° to the travelling direction of the car), to prevent the driver's trunk and head from hitting the steering wheel and rigid vehicle body parts in front of the driver, such as the frame posts or windscreen. The risk of this happening increases in inverse proportion to the size of the passenger compartment, i.e. the initial distance between the driver's trunk and head and the rigid vehicle body parts in front of the driver.
In a high-performance sports car, the size (particularly the height) of the passenger compartment is fairly small, to reduce the size of the front section of the car, and so increases the risk, in the event of a head-on or glancing collision without a seat belt, of the driver's trunk and head hitting the rigid vehicle body parts in front. To prevent this from happening, high-performance sports cars must therefore often be equipped with a high-volume driver's airbag (e.g. of at least 70 liters or even more). Using a high-volume driver's airbag, however, has drawbacks, by requiring a large, bulky airbag stowage compartment in the steering wheel hub, thus impairing the look of the steering wheel; and a high-power airbag inflation generator, which is more dangerous to the driver if the driver should be in an usual driving position, e.g. resting part of the body (such as a hand, forearm or head) on the steering wheel hub, when the airbag is inflated.